Sinter pallet apparatus

ABSTRACT

Sinter pallet apparatus including a frame supporting a plurality of coextensive grate bars formed with relatively thick structural support bodies which are spaced apart to define air passages therebetween. Relatively thin heat shields are arranged over the respective bars and spacers are provided for spacing such shields from such bars to form a heat insulator space between such bodies and shields. Insulating air is disposed in the insulator space and retainer means is included for retaining the shields on the bars.

United States Patent [191 [111 3,861,659

Evenstad Jan. 21, 1975 SINTER PALLET APPARATUS 3,548,763 12/1970 Farber266/21 x [75] Inventor: Sydney T. Evenstad El Monte 3,617,040 11/1971Relnfield et al. 266/21 C lif FOREIGN PATENTS OR APPLICATIONS [73]Assigneez Certified Auoy Products, Inc. g 347,461 4/1931 Great Britain266/21 UX B h, l'f. eac Primary Examiner-Gerald A. Dost [22] Filed: Oct27, 1972 Assistant Examiner-Paul A. Bell Attorney, Agent, orFirm-Fulwider, Patton, Rieber, [21] Appl. No.. 301,303 Lee & Utecht [52]US. Cl 266/21, 110/40 R, 432/241, 57 ABSTRACT 432/245 432/239 Sinterpallet apparatus including a frame supporting a y 53 plurality ofcoextensive grate bars formed with rela- 0 tively thick structuralsupport bodies which are spaced apart to define air passagestherebetween. Relatively [56] R f n Ct d thin heat shields are arrangedover the respective bars e are ces l e and spacers are provided forspacing such shields from UNITED STATES PATENTS such bars to form a heatinsulator space between such 311,633 2/1885 bodies and shields.Insulating air is disposed in the in- 1,889,052 11/1932 sulator spaceand retainer means is included for re- ?322682 13323 aining the shieldson the bars, 3:420:512 1/1969 9 Claims, 15 Drawing Figures Patented Jan.21, 1975 3 Sheets-Sheet 2 FIG.

Patented Jan. 21, 1975 3 Sheets-Sheet :5

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FIGJI SINTER PALLET APPARATUS BACKGROUND OF THE INVENTION 1. Field ofthe Invention The sinter pallet apparatus of the present inventionrelates to a pallet for conveying metallic pellets through a heat zonefor heating thereof to relatively high temperatures.

2. Description of the Prior Art Numerous sinter pallets have beenproposed which include coextensive grate bars spaced apart to define airpassages therebetween. Further, covers have been proposed for such gratebars in attempt to protect such grate bars against wear. However, suchprior art devices suffer the shortcomings that the grate bars arenecessarily relatively thick and are exposed to the heat of the pelletscarried thereon thus resulting in a high temperature differentialthroughout the thickness of such grate bars which results in excessivethermal growth on one side thereof thus causing warpage and thermalfatigue.

SUMMARY OF THE INVENTION The sinter pallet of the present invention ischaracterized by a plurality of relatively thick coextensive grate barshaving relatively thin heat shields disposed thereover and spacedtherefrom to form an insulator space having insulation disposed thereinto insulate the thick bars from the high temperature of the relativelythin heat shields. Consequently, the heat shields are heated relativelyrapidly to a substantially uniform temperature thus avoiding excessivetemperature differential throughout the thickness thereof and theconsequence warping due to non-uniform thermal growth.

The objects and advantages of the present invention will become apparentfrom a consideration of the following detailed description when taken inconjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagramatic view of a palletconveyor employing a sinter pallet apparatus embodying the presentinvention;

FIG. 2 is a top view, in enlarged scale, of a sinter pallet apparatusincluded in the conveyor shown in FIG.

FIG. 3 is a vertical sectional view, in enlarged scale, taken along theline 3-3 of FIG. 2;

FIG. 4 is a vertical sectional view, in enlarged scale, taken along theline 4-4 of FIG. 2;

FIG. 5 is a vertical sectional view, in enlarged scale, taken along theline 5-5 of, FIG. 2;

FIG. 6 is a top view of a second embodiment of the sinter palletapparatus of the present invention;

FIG. 7 is a vertical sectional view, in enlarged scale, taken along theline 7-7 of FIG. 6;

FIGS. 8 and 9 are vertical sectional views, in enlarged scale, takenalong the respective lines 8-8 and 99 of FIG. 6;

FIG. 10 is a vertical sectional view taken through a third embodiment ofthe sinter pallet apparatus of the present invention;

FIG. 11 is a horizontal sectional view taken along the line 11-11 ofFIG. 10;

FIG. 12 is a vertical sectional view, in enlarged scale, taken along theline 12-l2 of FIG. 11;

FIG. 13 is a vertical sectional view taken through a fourth embodimentof the sinter pallet apparatus of the present invention; and

FIGS. 14 and 15 are vertical sectional views, in enlarged scale, takenalong the line 14l4 of FIG. 13 with FIG. 15 depicting a heat shieldunlatched for removal thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 2, 3 and 4,the sinter pallet apparatus, generally designated 20, of the presentinvention includes a rectangularly shaped pallet frame 21 having aplurality of elongated grate bars disposed longitudinally therein inparallel arrangement. Referring to FIG. 3, the grate bars 23 include arelatively thick body 25 which has upwardly projecting bosses 27 formedtherein, such bosses including longitudinally extending open endeddovetail grooves 29 (FIG. 4). Relatively thin slat-like heat shields 31are spaced above the grate bar bodies 25 to form air spaces 33 betweensuch bodies and the bodies of the grates 25. The heat shields 31 includedownwardly projecting dovetail tongues 35 which slide longitudinallyinto the respective grooves 29 for securing the heat shields 31 inplace. The grate bar bodies 25 are themselves spaced apart and therespective heat shields 31 are formed in their opposite longitudinaledges with cutbacks which are disposed in confrontation with one anotherto form vertically extending through flow passages 37. Thus, the slats23 combine to form a permeable platform for receipt of pellets 41 to besintered, and such pellets are passed beneath a high temperatureinverted furnace 43 which rapidly raises the temperature of such pellets41 thus resulting in rapidly raising the temperature of the heat shields31. However, the relatively massive structural bodies 25 of therespective grate'bars 23 are insulated from the high temperature heatshield 31 by means of the insulative air in the air gaps 33 between thebody of such grate bar bodies 25 and the heat shields 31 thus enablingthe relatively massive grate bar bodies 25 to remain at a relativelyuniform temperature to thus prevent excessive thermal growth on the topside thereof which may result in warpage and even thermal fatigue.

In the processing of certain ore, the ore is pulverized and subsequentlyformed into individual balls or pellets 41. The pellets are subsequentlycharged into gas furnace and cooperate together to form air passagestherearound to facilitate heating thereof. In order to hold the pellets41 in their pelletized configuration, it is necessary to heat them to ahigh temperature. Thus, after formation thereof, the pellets 41 are fedfrom a hopper 44 onto the bed formed by air permeable pallets 20 carried on a conveyor, generally designated 51, to be passed beneath aninverted furnace 43 which heats such pellets to temperatures in theneighborhood of 2,400F. Consequently, the grate bars forming the airpermeable pallets 20 are subjected to extremely high temperatures ontheir top sides thus frequently resulting in such bars becoming warpeddue to non-uniform thermal growth. Consequently, it is desirable toprovide an air permeable pallet 20 which has an extremely tough abrasionresistant bed for receipt of the abrasive pellets 41 and which providesfor long life of such bars without warpage or thermal fatigue. I

The pallets 20 include rectangular frames 21 which are carried on theiropposite sides from wheels 55 and 57 which travel in respective conveyortracks 59 and 61. The pallet frames 21 are formed at their front andrear extremities with respective rails 63 and 65 which receive theopposite ends of the respective grate bars 23, the rail 65 beingremovable for selective removal of the grate bars 23. The opposite endsof the grate bar bodies 25 are bifurcated to form downwardly andoutwardly projecting fingers 69 and 71 for receipt under the respectiverails 65 and 63 to hold such grate bars in place.

As employed herein the term grate bar" refers to a rather heavy bodiedbar which is conventionally mounted on a pallet to receive the pellets41 directly thereon for heating thereof. The grate bars 23 are formed ontheir opposite sides with spacers 67 which project from the grate barbodies 25 approximately one-eighth of an inch for abutting against oneanother to cooperate in forming air passages 68 (FIG. between suchspacers 67 that are approximately onefourth of an inch in width. Thegrate bar body is approximately 1 inch in width and approximately 1%inches in vertical thickness thereby providing a relatively massivestructure. In contrast, the heat shield 31 is approximately 0.20 inchesthick and 1 inch wide.

The bosses 27 project upwardly from the top surface of the grate barbodies 25 approximately one-fourth of an inch and are themselvesapproximately threefourths of an inch long in the longitudinal directionof the grate bar 23 and are spaced apart approximately 2 inches thusproviding air spaces 33 having a dimension of approximately one-fourthinch thick by 2 inches in length.

The heat shields 31 may be made of various exotic or treated metals thatwill withstand high temperatures and those shown in the preferredembodiment are made of an alloy designated 2512 which includes 25percent chrome and 12 percent nickel. Further, in applications wheresulphur fumes are present, it has been found that such shields 31perform particularly well when constructed of 2512 alloy to provide atough core and then plating such cores with 98 chrome to a thickness ofapproximately 5 mills.

Referring to FIG. 4, the heat shields 31 are formed from a generallyflat elongated slat 73 with the respective tongues 35 projectingdownwardly therefrom, such tongues being slightly longer in verticallength than the depth of the grooves 29 whereby such tongues will act tosupport theheat shields 31 from the bottom of the respective grooves 29.It will be appreciated that each tongue 35 is approximatelythree-fourths of an inch in horizontal length with such tongues beingspaced apart approximately 2 inches thus aligning each tongue in itsrespective groove 29.

Referring to FIGS. 2 and 5, the heat shield slats 73 are formed in theiropposite sides with spaced apart cutbacks 45 which align together toform the respective vertical air passages 37, such air passages beingapproximately 2 inches in length and one-fourth of an inch in width.Referring particularly to FIG. 5, the cutbacks 45 are formed with adownwardly and inwardly slanted vertical surface thus causing thecutbacks 45 of adjacent slats 73 to cooperate together in forming avertically extending through air passage 37 which tapers downwardly andoutwardly on its opposite sides thus providing a configuration wherebyany pellets 41 passing into the top end of such passage fallingdownwardly through such passage to pass freely from the bottom thereof.

Referring to FIG. 1, when it is desirable to heat the pellets 41, theindividual pallets 20 are placed in the tracks 59 and 61 forming theconveyor 51, and such conveyor started to commence travel of suchpallets horizontally from left to right as viewed in FIG. 1. Theinverted furnace 43 is started to develop a high temperature gas to bedrawn downwardly through the pellets 41 and permeable pallets 20 bymeans of a wind box 79.

A rapper may be provided for rapping each pallet 20 as it passes therebyto thus knock any pellets 41 remaining thereon loose before recommencingtravel to the inverted furnace 43. In certain instances it is desirableto provide a hopper 87 of sintered pellets 89 ahead of the raw pellethopper 44 for distribution of such pellets 89 onto the pallets 20 toform a hearth layer of protective pellets thereover to protect the heatshields 31 from the excessively high temperature to which the unsinteredpellets 41 are to be heated. However, for most present day applications,with the pallet apparatus of the present invention, there is nonecessity of providing a hearth layer of protective pellets 89. However,for the purpose of this description, it will be assumed that such hearthlayer is distributed on the pallets 20.

The pallets 20 are caused to move along the conveyor tracks 59 and 61 bymeans of a prime mover, such as a motor driven oversized sprocket whichsequentially engages the respective pallets 20 and urges them along suchtracks. As the pallets 20 pass under the hearth hopper 87, the sinteredpellets 89 will be distributed over the bed formed by the composite heatshields 31 to form a hearth layer approximately 3 to 5 inches thick.

The pallets 20 having the hearth layer of pellets 89 are then passedbeneath the hopper 44 of raw pellets 41 to have such raw pelletsdistributed over the hearth layer. The pellets 41 are then conveyedbeneath the inverted furnace 43 and the wind box 79 will create apartial vacuum beneath such pallets 20 to cause the heated gases fromsuch furnace to flow downwardly through the passages formed between thepellets 41 and 89 to flow through the passages 37 formed between theheat shields 31 and then downwardly through the passages 68 formedbetween the respective grate bar bodies 25, it being appreciated that asubstantial amount of the heat of the gases from the furnace 43 isremoved by the pellets 41 and 89 and the heat shields 31 before suchgases contact the grate bar bodies 25. As the pallets 20 progress underthe furnace 43, the pellets 41 and 89 will become heated and the heatshields 31 may become heated to temperatures in the order of 2,000F.

However the relatively, stagnant air which is isolated within theinsulator spaces 33 (FIG. 3) formed between the heat shield slats 73 andthe grate bodies 25 provides a relatively low rate of heat transferbetween the slats 73 and grate bars 23 thus forming an excellent heatinsulator which results in the temperature of such grate bar bodies 25being approximately 500F. to 700F. lower than the temperature of theheat shields 31. Consequently, the grate bars 23 are subjected torelatively constant temperatures throughout their 2 inch verticalthicknesses thus avoiding excessive differential thermal growth andconsequent warpage and thermal fatigue from repeated heating. Incontrast, the relatively thin heat shields 31 will be heated relativelyrapidly and uniformly thus preventing warpage thereof, it beingappreciated that the tongues 35 (FIG. 4) are free to 'slidelongitudinally within the grooves 29 thus accommodating longitudinalthermal growth of such heat shields 31 relative to the grate bars 23. Itshould be noted that the relatively rapid heating of the heat shields 31to high temperatures greatly facilitates heating of the pellets 41 sincethe heat from such shields is reflected back toward such pellets.

As the respective pallets pass from beneath the furnace 43, such palletswill be tipped to an inverted position as they pass thus exposing thepellets 41 and 89 to cooling air and dumping such pellets onto thedelivery conveyor 83. As the pallets 20 are conveyed back to thestarting point in their inverted positions, such pallets will coolsubstantially before they again reach the furnace 43. As the pallets 20pass in front of the rapper 85, each pallet will be rapped one or moretimes to jar the respective heat shields 31 to free any pellets 89 or 41that may be stuck thereto or which may have wedged therebetween. It hasbeen found that the bosses 27 carrying the shield tongues 35 provideadequate support for such shields against the force of the rapper 85.

If at any time the heat shields 73 become excessively worn or warped,such heat shields may conveniently be replaced by sliding such shieldslongitudinally with respect to the grate bars to move the respectivetongues 35 clear of the grooves 29 (FIG. 4) to free such heat shield 31from its grate bar 23. Such heat shield 31 may then be replaced by arepaired or new heat shield 31 by merely sliding such heat shield intoposition. It will be appreciated that the grate bars 23 may weighbetween 5 and 9 pounds while the heat shields 31 weigh approximatelyonly 1% pounds thus resulting in substantial metal saving each timereplacement is required and rendering the taskof replacement mucheasier. In practice, the sintered pallet apparatus of the presentinvention has proven to provide a cost savings of between 75 percent and400 percent per ton of sintered ore.

Referring to FIG. 6, the sintered pallets, generally designated 91,showntherein are generally similar to the pallets 20 shown in FIG. 2 exceptthat the opposite ends of the grate bars, generally designated 93, areformed with vertically facing upwardly and outwardly opening cavities 94(FIG. 7) which receive downwardly projecting fingers 95 formedintegrally with respective heat shields, generally designated 97.Further, the heat shields 97 are formed with downwardly projectingsupports 99 which are disposed intermediate the respective tongues 101(FIG. 8). It will be noted that the heat shields 97 span onlyapproximately one-half the total length of the respective grate bars 93,the proximate free ends of such grate bars 97 being free floating andformed with downwardly and inwardly inclined ends 103 which cause anypellets 41 lodged therebetween to be urged upwardly thereout of as therespective shields 97 are heated and grow in length resulting in theproximate ends thereof being driven closer together.

Thus, operation of the sinter pallet apparatus shown in FIGS. 6 through9 is substantially the same as that described hereinabove, and airtrapped in the insulator space 105 formed between the underside of theheat shields 97 and the top of the body of the grate bars 93 will serveto thermally insulate the grate bars 93 from the heat of the respectiveheat shields. Further, the supports 99 will provide additional supportto the shields 97 to resist the shock introduced by the rapper as suchshields 97 are rapped.

The sinter pallet apparatus, generally designated 109, shown in FIGS. 10through 12, is similar to that described hereinbove except that thegrate bar, generally designated 111, is formed at its opposite ends withupwardly projecting ears 113 and 115 which are formed with inwardlyopening grooves 117 and 119, respectively. The grate bar 111 is furtherformed centrally with an upward projection which is formed in itsopposite sides with horizontal grooves 121 and 123 aligned horizontallywith the respective grooves 117 and 119 for receipt of the opposite endsof respective slat like heat shields 127. The grate bars 111 are furtherformed in their opposite halves with intermediately located upwardlyopening dovetail grooves 131 and 133 which receive downwardly projectingdovetail tongues 132 and 134 which provide support against the rapper85.

Referring to FIGS. 11 and 12, the heat shields 127 and 129 are formed intheir opposite sides with longitudinal cut-outs which cooperate to formvertically through air passages 135 which extend substantially the fulllength of such heat shields 127 and 129, the edges of such cut-outsbeing slanted downwardly and inwardly as shown in FIG. 12 to form suchpassages 135 with bottom openings that are larger in cross section thanthe top openings thereof. Again, this arrangement facilitates release ofany pellets 41 or 89 which might pass downwardly into the respectivepassages 135. Consequently, operation of the pallet 109 is substantiallythe same as that set forth hereinabove with the grate bar 111 beingthermally insulated from the respective heat shields 127 and 129 duringsintering of pellets located thereon.

The sinter pallet, generally designated 139 shown in FIG. 13, provides arelatively convenient means for securing heat shields, generallydesignated 141 and 143, to grate bars 145. The grate bars 145 are formedin their opposite extremities with upwardly projecting bosses 147 and149, an intermediate boss 151 being formed therebetween. The bosses 147,149 and 151 are all formed with longitudinally extending cylindricalkeyway cavities 153 (FIGS. 14 and 15) which have areduced-in-cross-section chordal opening in the tops thereof definingrelatively narrow keyway necks 155. The heat shields 141 are formed withslats 157 having downwardly projecting key elements projecting therefromand formed in their bottom extremities with cylindrically shaped stops159 which are cut off along chordal lines at their upper and lowerextremities to form an upper cut-back 161 and a lower chordal side 163.Thus, the bosses 147, 149 and 151 support the slats 157 elevated fromthe body of the grate bar 145 to form insulator spaces 167 which trapair to insulate the grate bars 145 from the heat shields 141.

The opposite edges of the slats 157 are cut on complementary slants 142to enable such slats to be nested together as shown in FIG. 14.

Operation of the sinter pallet apparatus 139 shown in FIGS. 13 through15 is substantially the same as set forth hereinabove except that therespective heat shields 141 and 143'may conveniently be removed bymerely lifting the free edges thereof to essentially unbutton the stops159 from the retainer cavities 153 as shown in FIG. 15 to enable suchshields to be lifted freeof the grate bars 145 for convenientreplacement thereof.

From the foregoing, it will be apparent that the sinter pallet apparatusof the present invention provides a convenient and economical means forconveying pellets through a high temperature zone for sintering thereof.The pallet apparatus provides for a long and trouble-free service lifeand substantially reduces the cost of replacing worn or warped elements.

I claim:

1. Sinter pallet apparatus comprising:

a frame including a pair of coextensive rail means;

a plurality of elongated coextensive grate bars projecting between saidrail means and formed with relatively thick structural support bodiesspaced apart transversely to form flow passages therebetween, said gratebars having top and bottom sides and being formed on said respective topsides with respective first retaining elements spaced longitudinallytherealong;

a plurality of elongated heat shields including relatively thin flatslats disposed above and projecting parallel with said respective gratebars and formed with respective second retaining elements projectingfrom the bottom sides thereof received in said respective firstretaining elements to lock said respective heat shields on saidrespective grate bars, said second retaining elements having relativelysmall horizontal cross sections; and

spacer means projecting from said heat shields and spacing saidrespective heat shields from the respective bodies of said grate bars toform heat insulator spaces between the respective bodies of said gratebars and said heat shield slats, said spacer means and second retainingelements cooperating to form said spaces with relatively largehorizontal dimensions in the longitudinal directions of said heatshields whereby sintered pellets may be received on said heat shieldsfor conveyance under a furnace directing heat thereonto and heating ofsaid pellets to a relatively high temperature will result in heating ofsaid heat shields to a relatively high temperature while air trapped insaid insulator spaces will act as an insulator to resist direct transferof heat from said shields to said respective grate bars to therebypermit said respective grate bars to remain at a relatively lowtemperature.

2. Sinter pallet apparatus as set forth in claim 1 wherein:

said spacer means space said respective heat shields from saidrespective grate bodies at least oneeighth of an inch.

3. Sinter pallet apparatus as set forth in claim 1 wherein:

said heat shields are formed on their opposite sides with longitudinalcut-backs which form open bottom heat passages having sides which angledownwardly and inwardly whereby pellets wedged into the top of said heatpassages will fall freely downwardly therethrough.

4. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bar bodies are at least three times as thick as said heatshields.

5. Sinter pallet apparatus as set forth in claim 1 wherein:

said heat shields are constructed of 25 l 2 alloy plated withsubstantially 5 mills of 98 percent chrome. 6. Sinter pallet apparatusas set forth in claim 1 wherein:

said grate bars are formed on their opposite ends with upwardlyprojecting ears including horizontally projecting groove means whichopen inwardly to confront one another to define said respective firstretainer elements; and

said heat shields are of sufficient size to have their respectiveopposite extremities received in said respective groove means and beretained thereby.

7. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bars are formed with upwardly opening grooves defining saidfirst retaining elements, said slats being formed with respectivecavities having relatively large dimensions transverse to said gratebars and being necked down towards the top thereof to form reduced incross section necks; and

said heat shields are formed with downwardly projecting tongues formingsaid second retaining elements and received in said respective groovesand being formed to closely fit said respective cross sections of saidcavities and then necking down to project through said respective necks.

8. Sinter pallet apparatus as set forth in claim 1 wherein:

said grate bars are formed with respective keyway cavities projectinglongitudinal of said respective bars and which are formed in their upperportions with circular cross sections transverse to said bars to formsaid first retaining elements, said cavities forming in excess of asemicylinder and opening along their top sides in chordal necks having adimension transverse to said bars which is less than the diameter ofsaid respective circular cross sections; and

said heat shields are formed with downwardly projecting keys received insaid respective keyway cavities and said keys are formed with stopswhich are circular in cross section to compliment the upper portion ofsaid keyways and are cut off horizontally below the horizontal diametersof said respective keyway cavities to form respective verticalthicknesses sufficiently small to, when the slats are rotated to projectvertically, fit through said respective necks, said slats projectingtransversely to the respective one sides of said respective keys andbeing cut back at their respective opposite sides to substantially thecenter of said keyway cavities to accommodate rotation of said keys insaid respective keyway cavities to enable said thickness thereof to fitout through said respective necks.

9. Sinter pallet apparatus as set forth in claim 8 wherein:

said slats project sufficiently far in said one direction to have thefree edges thereof received in the respective cutbacks of respectiveadjacent heat shields.

1. Sinter pallet apparatus comprising: a frame including a pair ofcoextensive rail means; a plurality of elongated coextensive grate barsprojecting between said rail means and formed with relatively thickstructural support bodies spaced apart transversely to form flowpassages therebetween, said grate bars having top and bottom sides andbeing formed on said respective top sides with respective firstretaining elements spaced longitudinally therealong; a plurality ofelongated heat shields including relatively thin flat slats disposedabove and projecting parallel with said respective grate bars and formedwith respective second retaining elements projecting from the bottomsides thereof received in said respective first retaining elements tolock said respective heat shields on said respective grate bars, saidsecond retaining elements having relatively small horizontal crosssections; and spacer means projecting from said heat shields and spacingsaid respective heat shields from the respective bodies of said gratebars to form heat insulator spaces between the respective bodies of saidgrate bars and said heat shield slats, said spacer means and secondretaining elements cooperating to form said spaces with relatively largehorizontal dimensions in the longitudinal directions of said heatshields whereby sintered pellets may be received on said heat shieldsfor conveyance under a furnace directing heat thereonto and heating ofsaid pellets to a relatively high temperature will result in heating ofsaid heat shields to a relatively high temperature while air trapped insaid insulator spaces will act as an insulator to resist direct transferof heat from said shields to said respective grate bars to therebypermit said respective grate bars to remain at a relatively lowtemperature.
 2. Sinter pAllet apparatus as set forth in claim 1 wherein:said spacer means space said respective heat shields from saidrespective grate bodies at least one-eighth of an inch.
 3. Sinter palletapparatus as set forth in claim 1 wherein: said heat shields are formedon their opposite sides with longitudinal cut-backs which form openbottom heat passages having sides which angle downwardly and inwardlywhereby pellets wedged into the top of said heat passages will fallfreely downwardly therethrough.
 4. Sinter pallet apparatus as set forthin claim 1 wherein: said grate bar bodies are at least three times asthick as said heat shields.
 5. Sinter pallet apparatus as set forth inclaim 1 wherein: said heat shields are constructed of 2512 alloy platedwith substantially 5 mills of 98 percent chrome.
 6. Sinter palletapparatus as set forth in claim 1 wherein: said grate bars are formed ontheir opposite ends with upwardly projecting ears including horizontallyprojecting groove means which open inwardly to confront one another todefine said respective first retainer elements; and said heat shieldsare of sufficient size to have their respective opposite extremitiesreceived in said respective groove means and be retained thereby. 7.Sinter pallet apparatus as set forth in claim 1 wherein: said grate barsare formed with upwardly opening grooves defining said first retainingelements, said slats being formed with respective cavities havingrelatively large dimensions transverse to said grate bars and beingnecked down towards the top thereof to form reduced in cross sectionnecks; and said heat shields are formed with downwardly projectingtongues forming said second retaining elements and received in saidrespective grooves and being formed to closely fit said respective crosssections of said cavities and then necking down to project through saidrespective necks.
 8. Sinter pallet apparatus as set forth in claim 1wherein: said grate bars are formed with respective keyway cavitiesprojecting longitudinal of said respective bars and which are formed intheir upper portions with circular cross sections transverse to saidbars to form said first retaining elements, said cavities forming inexcess of a semicylinder and opening along their top sides in chordalnecks having a dimension transverse to said bars which is less than thediameter of said respective circular cross sections; and said heatshields are formed with downwardly projecting keys received in saidrespective keyway cavities and said keys are formed with stops which arecircular in cross section to compliment the upper portion of saidkeyways and are cut off horizontally below the horizontal diameters ofsaid respective keyway cavities to form respective vertical thicknessessufficiently small to, when the slats are rotated to project vertically,fit through said respective necks, said slats projecting transversely tothe respective one sides of said respective keys and being cut back attheir respective opposite sides to substantially the center of saidkeyway cavities to accommodate rotation of said keys in said respectivekeyway cavities to enable said thickness thereof to fit out through saidrespective necks.
 9. Sinter pallet apparatus as set forth in claim 8wherein: said slats project sufficiently far in said one direction tohave the free edges thereof received in the respective cutbacks ofrespective adjacent heat shields.